90,967 research outputs found
Worldwide cloud cover model
Classifying worldwide cloudiness into homogeneous regions, using a satellite data set containing day IR, night IR, incoming, and absorbed solar radiation measurements on a 2.5-degree latitude-longitude grid is considered. Methods of analysis are presented
Vector wind profile gust model
The development of a vector wind gust model that is suitable for orbital flight test operations and trade studies was studied. Verification of the hypothesis that gust component variables are gamma distributed, gust modulus is approximately Weibull distributed, and zonal and meridional gust components are bivariate gamma distributed is emphasized. A method of testing for bivariate gamma distributed variables, and two distributions for gust modulus are described. The results of extensive hypothesis testing of one of the distributions are presented, and the validity of the gamma distribution for representation of gust component variables is established
A reference atmosphere for patrick afb, florida, annual /1963 revision/
Reference atmosphere for cape kennedy based on statistical parameters of pressure-height, temperature, and relative humidity at constant pressure level
Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars
The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained
Sensitivity analysis of the space shuttle to ascent wind profiles
A parametric sensitivity analysis of the space shuttle ascent flight to the wind profile is presented. Engineering systems parameters are obtained by flight simulations using wind profile models and samples of detailed (Jimsphere) wind profile measurements. The wind models used are the synthetic vector wind model, with and without the design gust, and a model of the vector wind change with respect to time. From these comparison analyses an insight is gained on the contribution of winds to ascent subsystems flight parameters
Atmospheric constraint statistics for the Space Shuttle mission planning
The procedures used to establish statistics of atmospheric constraints of interest to the Space Shuttle mission planning are presented. The statistics considered are for the frequency of occurrence, runs, and time conditional probabilities of several atmospheric constrants for each of the Space Shuttle mission phases. The mission phases considered are (1) prelaunch, (2) launch, (3) return to launch site, (4) abort once around landing, and (5) end of mission landing
Some properties of a 5-parameter bivariate probability distribution
A five-parameter bivariate gamma distribution having two shape parameters, two location parameters and a correlation parameter was developed. This more general bivariate gamma distribution reduces to the known four-parameter distribution. The five-parameter distribution gives a better fit to the gust data. The statistical properties of this general bivariate gamma distribution and a hypothesis test were investigated. Although these developments have come too late in the Shuttle program to be used directly as design criteria for ascent wind gust loads, the new wind gust model has helped to explain the wind profile conditions which cause large dynamic loads. Other potential applications of the newly developed five-parameter bivariate gamma distribution are in the areas of reliability theory, signal noise, and vibration mechanics
Unitarity of theories containing fractional powers of the d'Alembertian operator
We examine the unitarity of a class of generalized Maxwell U(1) gauge
theories in (2+1) D containing the pseudodifferential operator
, for . We show that only Quantum
Electrodynamics (QED) and its generalization known as Pseudo Quantum
Electrodynamics (PQED), for which and , respectively,
satisfy unitarity. The latter plays an important role in the description of the
electromagnetic interactions of charged particles confined to a plane, such as
in graphene or in hetero-junctions displaying the quantum Hall effect.Comment: 6 pages, no figure
Interaction Induced Quantum Valley Hall Effect in Graphene
We use Pseudo Quantum Electrodynamics (PQED) in order to describe the full
electromagnetic interaction of the p-electrons of graphene in a consistent 2D
formulation. We first consider the effect of this interaction in the vacuum
polarization tensor or, equivalently, in the current correlator. This allows us
to obtain the dc conductivity after a smooth zero-frequency limit is taken in
Kubo's formula.Thereby, we obtain the usual expression for the minimal
conductivity plus corrections due to the interaction that bring it closer to
the experimental value. We then predict the onset of an interaction-driven
spontaneous Quantum Valley Hall effect (QVHE) below a critical temperature of
the order of K. The transverse (Hall) valley conductivity is evaluated
exactly and shown to coincide with the one in the usual Quantum Hall effect.
Finally, by considering the effects of PQED, we show that the electron
self-energy is such that a set of P- and T- symmetric gapped electron energy
eigenstates are dynamically generated, in association with the QVHE.Comment: 5 pages + supplemental materia
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